The invention relates generally to hydraulic circuitry and, more specifically, to an oil cooling circuit for continuously reciprocating hydraulic cylinders.
Hydraulic cylinders are used in a wide variety of applications. In certain applications, particularly high pressure, high duty applications, the hydraulic fluid may reach temperatures that begin to degrade components of the hydraulic circuitry and adversely affect performance of the hydraulic cylinders and associated equipment. In particular, some continuously reciprocating high-pressure cylinders currently experience higher than normal rod seal failure. Because these systems have high costs of construction and operation, repair and replacement of components as a result of heat damage is expensive not only in the cost of replacement components and the labor required for the repair but also in the downtime of the equipment.
Hydraulic fluid builds up heat if it is doing work but is not able to travel out to an oil cooler. Heat buildup is due to fluid friction and the thermodynamic effect (adiabatic heating) of being repeatedly compressed during each cylinder cycle. Depending on the displacement of the cylinder and the length and diameter of the fluid lines that power the cylinder, a certain percentage of this oil is trapped and merely travels back and forth in the fluid lines connected to the work ports of the cylinder. Hydraulic oil has a compressibility of approximately 0.5 percent per 1000 psi of pressure. If the hose or tubing carrying the high pressure oil from the pump to the cylinder has sufficient length that a significant percentage of the oil volume required for that stroke never leaves the hose or tubing, this trapped oil cannot circulate out for cooling and heat builds up incrementally during operation. A certain amount of mixing and heat transfer with cooler, in-coming oil most likely occurs but the oil closest to the cylinder piston remains at a high temperature and in an unfiltered condition. As the linear distance between the pump or valve and the cylinder is increased, and as the cylinder displacement is increased, the problem becomes more severe.
There is a need, accordingly, for a means of cooling the hydraulic fluid in such systems to avoid the high temperatures that adversely affect performance, the cost of operation, and the costs of repairs.